Likes

Search

InfraRed Zooms

I’ve been looking into sources for zoom lenses that have been coated for InfraRed shooting - or how difficult it would be to coat lenses for it.

We did a shoot recently using Panasonic LT’s with the IR-cut filter removed, as well as a Canon ME20 (mostly in visible light mode and at ridiculously high ISO, but it also easily flips out the IR-cut filter with a simple menu selection).

The issue is when using IR LED’s that are in the shot (or any source that gives off a decent amount of IR)… you get some pretty bad internal reflections, because the lenses are coated for the 350-750’ish nm range - and we’re letting the higher wavelengths get to the sensor.

So I wanted to gather sources and info on coating lenses for IR reflections.

Say a 24-290, 18-85 or a 19-90 cabrio, just as some examples of what could be needed.

Prime lenses were somewhat better (less elements) but still not immune.

It only takes one internal “mirror” to give an annoying / offset of a hotter IR source in the frame.

But the show would really need a few zooms so that’s the main goal.

In this case, any lens darkening due to the coating would be trivial - we have plenty of IR light to light for it.

That HSK filter seems to do the trick at the sensor level, but judging from what I saw and how the reflections moved with pan/tilt and zoom, the worst reflections were within the zoom elements - and it was only one element in particular. That’s what made me wonder if coating at least that one offending element would do the trick (this was a 19-90 cabrio).

Or if any pro lenses exist for larger sensors that have already coated for this.

Or if any pro lenses exist for larger sensors that have already coated for this.

Might be worth a call or email to Dan Sasaki at PV Woodland Hills - I know that PV has done military contract stuff in the past and they’ve done a number of odd night-vision things that would have been very IR touchy.

I’ve been looking into sources for zoom lenses that have been coated for InfraRed shooting - or how difficult it would be to coat lenses for it.

I have done a lot of work shooting IR. There is a fundamental issue with zoom lenses that in most cases make them unsuitable for use with infra red illumination. It comes back to the fact lenses are designed and optimized for visible wavelengths. The much longer wavelengths of near infra red, 0.75–1.4 µm means that the spacing between lens elements is not optimized for the wavelengths used with IR illumination. Given zoom lenses have many more elements than prime lenses this causes more issues, often halos, flares and generally soft images. So I generally stay clear of zoom lenses for this reason.

There is also an issue caused by internal reflections from the interior of the lens barrels when IR light is reflected where visible light is absorbed. Again causing flares and halos and central spots.

I find that generally simpler the lens design the better the results. I my experience often older prime lenses give best results, especially early Zeiss prime series or older (FD series) long (300mm plus) Canon prime still lenses seem to work quite well. (possibly because of simpler coatings or barrel design)

It is also advisable to use IR band pass filters in front of the lens to block visible light and only allow the specific IR wavelengths you want to pass.

There is also an issue caused by internal reflections from the interior of the lens barrels when IR light is reflected where visible light is absorbed. Again causing flares and halos and central spots.

I second this, go with the most simple optical design lenses you can find and you'll be better off than with more complicated. With the hotspots your only practical solution generally is to change your angle in relation to the angle of light entering the lens, but that may not be possible depending on what you are shooting.

Verify Delete

Are you sure you wish to delete this message from the message archives of cml-glass@cml.news? This cannot be undone.

Report Message

Reason

Report to Moderators
I think this message isn't appropriate for our Group. The Group moderators are responsible for maintaining their community and can address these issues.
Report to CML Support
I think this violates the Terms of Service. This includes: harm to minors, violence or threats, harassment or privacy invasion, impersonation or misrepresentation, fraud or phishing.